Abstract
The development of blue-emissive InP quantum dots (QDs) still lags behind that of the red and green QDs because of the difficulty in controlling the reactivity of the small InP core. In this study, the reaction kinetics of the ZnS shell was controlled by varying the length of the hydrocarbon chain in alkanethiols for the synthesis of the small InP core. The reactive alkanethiol with a short hydrocarbon chain forms the ZnS shell rapidly and prevents the growth of the InP core, thus reducing the emission wavelength. In addition, the length of the hydrocarbon chain in the fatty acid was varied to reduce the nucleation kinetics of the core. The fatty acid with a long hydrocarbon chain exhibited a long emission wavelength as a result of the rapid nucleation and growth, due to the insufficient In–P–Zn complex by the steric effect. Blue-emissive InP/GaP/ZnS QDs were synthesized with hexanethiol and lauryl acid, exhibiting a photoluminescence (PL) peak of 485 nm with a full width at half-maximum of 52 nm and a photoluminescence quantum yield of 45%. The all-solution processed quantum dot light-emitting diodes were fabricated by employing the aforementioned blue-emissive QDs as an emitting layer, and the resulting device exhibited a peak luminance of 1045 cd/m2, a current efficiency of 3.6 cd/A, and an external quantum efficiency of 1.0%.
Highlights
Colloidal quantum dots (QDs) have received significant attention as promising emitting materials for next-generation display devices owing to their outstanding color purity, convenient color tunability, near-unity photoluminescence quantum yield (PLQY), and low-cost solution processability [1,2,3,4,5,6]
These results indicate that a short and reactive alkanethiol forms the ZnS shell rapidly and prevents the growth of the Indium phosphide (InP) core, reducing the emission wavelength
S-TOP is commonly used for ZnS shell formation; the PL emission peak of the QD prepared with S-TOP shifted to a longer wavelength of 517 nm, indicating that S-TOP slows down the ZnS shell growth due to lower reactivity, resulting in further growth of the core
Summary
Colloidal quantum dots (QDs) have received significant attention as promising emitting materials for next-generation display devices owing to their outstanding color purity, convenient color tunability, near-unity photoluminescence quantum yield (PLQY), and low-cost solution processability [1,2,3,4,5,6]. Indium phosphide (InP) QDs are considered to be an environmentally friendly alternative because of their relatively low toxicity and emission wavelength covering most visible wavelengths. The synthesis of InP QDs is, relatively challenging compared with that of Cd QDs because of their covalent character, vulnerability to oxidizing environments, and lattice mismatch between the InP core and ZnS shell. The optical properties of InP QDs have been improved by the introduction of inner shells such as ZnSe [14,15,16], ZnSeS [17,18,19,20], and GaP [21,22,23] to alleviate abrupt interfacial strain and the removal of the oxide surface of the InP core through in situ etching [15,16]. The small InP cores are difficult to passivate because of their large surface-to-volume ratio [24,25,26]
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